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Improved sterile neutrino constraints from the STEREO experiment with 179 days of reactor-on data

H. Almazán1, L. Bernard2,‡, A. Blanchet3,§, A. Bonhomme1,3, C. Buck1, P. del Amo Sanchez4, I. El Atmani3,∥, J. Haser1, F. Kandzia5 et al. (STEREO Collaboration†)

F. Kandzia5, S. Kox2, L. Labit4, J. Lamblin2, A. Letourneau3, D. Lhuillier3, M. Licciardi2, M. Lindner1, T. Materna3, A. Minotti3,¶, H. Pessard4, J.-S. Réal2, C. Roca1, R. Rogly3, T. Salagnac2,**, V. Savu3, S. Schoppmann1,*, V. Sergeyeva4,††, T. Soldner5, A. Stutz2, and M. Vialat5 (STEREO Collaboration†)

  • 1Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
  • 2Université Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 38000 Grenoble, France
  • 3IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
  • 4Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS/IN2P3, LAPP, 74000 Annecy, France
  • 5Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France

  • *stefan.schoppmann@mpi-hd.mpg.de
  • †http://www.stereo-experiment.org.
  • ‡Present Address: Ecole Polytechnique, CNRS/IN2P3, Laboratoire Leprince-Ringuet, 91128 Palaiseau, France.
  • §Present Address: LPNHE, Sorbonne Université, Université de Paris, CNRS/IN2P3, 75005 Paris, France.
  • ∥Present Address: Hassan II University, Faculty of Sciences, Aïn Chock, BP 5366 Maarif, Casablanca 20100, Morocco.
  • Present Address: Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS/IN2P3, LAPP, 74000 Annecy, France.
  • **Present Address: Institut de Physique Nucléaire de Lyon, CNRS/IN2P3, Université Lyon, Université Lyon 1, 69622 Villeurbanne, France.
  • ††Present Address: Institut de Physique Nucléaire Orsay, CNRS/IN2P3, 15 rue Georges Clemenceau, 91406 Orsay, France.
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Phys. Rev. D 102, 052002 – Published 9 September, 2020

DOI: https://doi.org/10.1103/PhysRevD.102.052002

Abstract

The STEREO experiment is a very short baseline reactor antineutrino experiment. It is designed to test the hypothesis of light sterile neutrinos being the cause of a deficit of the observed antineutrino interaction rate at short baselines with respect to the predicted rate, known as the reactor antineutrino anomaly. The STEREO experiment measures the antineutrino energy spectrum in six identical detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this article, results from 179 days of reactor turned on and 235 days of reactor turned off are reported at a high degree of detail. The current results include improvements in the modelling of detector optical properties and the γ-cascade after neutron captures by gadolinium, the treatment of backgrounds, and the statistical method of the oscillation analysis. Using a direct comparison between antineutrino spectra of all cells, largely independent of any flux prediction, we find the data compatible with the null oscillation hypothesis. The best-fit point of the reactor antineutrino anomaly is rejected at more than 99.9% C.L.

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Phys. Rev. D 102, 052002– Published 9 September, 2020
  • Received 16 December 2019
  • Accepted 31 July 2020
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